Contact Scheme Research Articles

Long-term stability in perovskite solar cells through atomic layer deposition of tin oxide.

Robust contact schemes that boost stability and simplify the production process are needed for perovskite solar cells (PSCs). We codeposited perovskite and hole-selective contact while protecting the perovskite to enable deposition of SnOx/Ag without the use of a fullerene. The SnOx, prepared through atomic layer deposition, serves as a durable inorganic electron transport layer. Tailoring the oxygen vacancy defects in the SnOx layer led to power conversion efficiencies (PCEs) of >25%. Our devices exhibit superior stability over conventional p-i-n PSCs, successfully meeting several benchmark stability tests. They retained >95% PCE after 2000 hours of continuous operation at their maximum power point under simulated AM1.5 illumination at 65°C. Additionally, they boast a certified T97 lifetime exceeding 1000 hours.

Tantalum doped tin oxide enabled indium-free silicon heterojunction solar cells with efficiency over 25 %

Reducing indium consumption has received increasing attention in contact schemes of high efficiency silicon heterojunction (SHJ) solar cells. It is imperative to discover suitable, low-cost, and resource-abundant transparent electrodes to replace the conventional, resource-scarce indium-based transparent electrodes. Herein, tantalum doped tin oxide (TTO), prepared through low-temperature sputtering, is selected as an alternative material. Notably, the Anti-Burstein-Moss effect of TTO is observed, which is ascribed to variations of stress in films. Based on this finding, TTO was first applied to SHJ solar cells, and the photoelectric tradeoff in front and rear contacts is gained by matching nanocrystalline silicon layers and adjusting TTO thickness. Ultimately, an indium-free SHJ solar cell with an efficiency of 25.15 % is obtained (certified efficiency 25.10 %, 274.30 cm2).

A dual-modified implicit time integration method for three-dimensional impact modelling within the framework of the SBFEM

This paper presents a dual-modified implicit time integration method (DMITIM) for three-dimensional impact modelling within the framework of the scaled boundary finite element method (SBFEM). Controlled by a single parameter, this method effectively dissipates high-frequency responses in impact problems without affecting low-frequency responses, ensuring time integration stability. To address the issue of false oscillations during impacts, additional Lagrange multipliers are introduced to supplement the velocity and acceleration corrections at each time integration step. For nonmatching meshes, by leveraging the mesh flexibility of the SBFEM, a rapid and straightforward remeshing method is utilized to establish a node-to-node contact scheme. The numerical results demonstrate that the DMITIM significantly reduces false oscillations in the velocity and contact force during impact events. It also showcases the flexibility of the SBFEM in handling nonmatching meshes. The combination of the SBFEM with the DMITIM provides enhanced simulation accuracy and stability for impact problems compared to the results from ABAQUS using the HHT-α time integration algorithm.

Si-implantation for Low Ohmic Contact Resistances in RF GaN HEMTs

Abstract In this work, Si implantation and activation for lowering the ohmic contact resistance (Rc) of mm-wave GaN HEMTs has been investigated. Various combinations of annealing temperature/duration and implantation doses were tested. Dopant activation was performed using a modified procedure in an MOCVD tool, involving fast temperature ramping and annealing the samples for 8 minutes at 1150 °C. Thereby, ~ 0.02 ± 0.01 Ω·mm contact resistance was achieved on a fully doped region and ~ 0.1 ± 0.02 Ω·mm when only the source and drain contact region was n-type doped. For comparison, a well-established alloyed Ti/Al/Ni/Au ohmic contact scheme without implantation, was used as reference resulting in an average Rc ~ 0.34 ± 0.12 Ω·mm on the same wafer. Besides the three times lowered contact resistance the implanted contacts also showed a significantly improved on-wafer homogeneity.

The dichotomous role of oxygen in the ohmic contact formation on p-type GaN grown by MBE and MOCVD

Molecular beam epitaxy (MBE) is often considered as an ideal equipment for growing low-resistance p-type GaN (p-GaN). However, the Ohmic contact formation mechanism of p-GaN grown by MBE is still unclear. In this work, MOCVD and MBE-grown p-GaN were prepared for contrastive analysis. We reported for the first time the different variation tendency in their electrical properties after annealing in the same ambient. Surface analyzing instruments were used to investigate the interfacial properties of p-GaN. Experimental results revealed that the oxygen in the annealing ambient had a negative effect on the Ohmic contact formation of MBE p-GaN, and the physical mechanism underlying it was figured out. It is proved that the annealing conditions for preparing Ohmic contacts on MOCVD p-GaN is not suitable for that on MBE p-GaN. To further reduce the effect of oxygen, an optimized Ohmic contact scheme for MBE p-GaN based on the Ni-Pd contact layer was proposed, which successfully reduced the specific contact resistivity (ρc) by two orders, to 8.6 × 10−5 Ω•cm2, compared with the conventional Pd/Pt/Au system. This research provides valuable guidance for device fabrication based on GaN grown by MBE and lays an essential foundation for preparing optoelectronic devices.

Ultra‐Lean Silver Screen‐Printing for Sustainable Terawatt‐Scale Photovoltaic

As the photovoltaics industry approaches the terawatt (TW) manufacturing scale, the consumption of silver in screen‐printed contacts must be significantly reduced for all cell architectures to avoid risks of depleting the global silver supply and substantial cost inflations. With alternative metallization techniques (e.g., plating) facing their own challenges for mass production, advancements in the mainstream screen‐printing technology to accelerate the pace of silver reductions are urgently needed. This work presents a silver‐lean screen‐printed contact scheme, providing scope for substantial reductions in silver consumption based on existing industrial screen‐printing capabilities. The initial testing of such a design leads to the fabrication of 24.04% efficient large‐area TOPCon solar cells with 9 mg W−1 silver consumption compatible with existing soldering‐based interconnection technologies, corresponding to a 25%rel reduction in silver usage compared to standard industrial screen‐printed TOPCon solar cells. Upon further optimization in pattern designs and fabrication processes, this silver‐lean design offers a promising pathway toward ultra‐low silver consumption of less than 2 mg W−1 for screen‐printed TOPCon solar cells without sacrificing efficiency.

Antimony-Platinum Modulated Contact Enabling Majority Carrier Polarity Selection on a Monolayer Tungsten Diselenide Channel.

We develop a novel metal contact approach using an antimony (Sb)-platinum (Pt) bilayer to mitigate Fermi-level pinning in 2D transition metal dichalcogenide channels. This strategy allows for control over the transport polarity in monolayer WSe2 devices. By adjustment of the Sb interfacial layer thickness from 10 to 30 nm, the effective work function of the contact/WSe2 interface can be tuned from 4.42 eV (p-type) to 4.19 eV (n-type), enabling selectable n-/p-FET operation in enhancement mode. The shift in effective work function is linked to Sb-Se bond formation and an emerging n-doping effect. This work demonstrates high-performance n- and p-FETs with a single WSe2 channel through Sb-Pt contact modulation. After oxide encapsulation, the maximum current density at |VD| = 1 V reaches 170 μA/μm for p-FET and 165 μA/μm for n-FET. This approach shows promise for cost-effective CMOS transistor applications using a single channel material and metal contact scheme.

Charge-transfer contacts for the measurement of correlated states in high-mobility WSe2.

Two-dimensional semiconductors, such as transition metal dichalcogenides, have demonstrated tremendous promise for the development of highly tunable quantum devices. Realizing this potential requires low-resistance electrical contacts that perform well at low temperatures and low densities where quantum properties are relevant. Here we present a new device architecture for two-dimensional semiconductors that utilizes a charge-transfer layer to achieve large hole doping in the contact region, and implement this technique to measure the magnetotransport properties of high-purity monolayer WSe2. We measure a record-high hole mobility of 80,000 cm2 V-1 s-1 and access channel carrier densities as low as 1.6 × 1011 cm-2, an order of magnitude lower than previously achievable. Our ability to realize transparent contact to high-mobility devices at low density enables transport measurements of correlation-driven quantum phases including the observation of a low-temperature metal-insulator transition in a density and temperature regime where Wigner crystal formation is expected and the observation of the fractional quantum Hall effect under large magnetic fields. The charge-transfer contact scheme enables the discovery and manipulation of new quantum phenomena in two-dimensional semiconductors and their heterostructures.

Thinning Solution‐proceed 2D Te for p‐ and n‐channel Junction Field Effect Transistor with High Mobility and Ideal Subthreshold Slope

AbstractTwo‐dimensional non‐layered tellurene (Te) can serve as a promising candidate in transistor applications because of its high carrier mobility and air stability. However, it is still quite challenging in aspect of ultra‐thin channel and gate‐control ability in conventional metal‐oxide‐semiconductor field‐effect transistor architecture. This work proposes a facile thinning strategy for solution‐proceed Te flakes and fabricates a junction field‐effect transistor (JFET) architecture, that has well addressed the above‐mentioned two issues. Through a mild oxidative thinning process, the post‐growth Te flakes are thinned from bulk to few‐layer, guaranteeing the highly efficient electrostatic doping as a transistor channel. Then, a four‐terminal JFET‐based on p‐Te and n‐ReS2 is designed, achieving a multifunctional integration of rectification diode, p‐ and n‐channel transistor in one single device. By accessing different contact scheme, the ReS2/Te p‐n diode is explored with a rectification ratio of 103, the p‐channel JFET exhibits a high hole mobility of 317.6 cm2V−1s−1, ideal low subthreshold swing of 84 mV dec−1. While the n‐channel JFET is obtained with electron mobility of 67.6 cm2 V−1s−1 and SS of 229 mV dec−1. Both p‐ and n‐channel devices showcase clear saturation characteristic with ultra‐small pinch‐off voltage (≈0.4 V), which is crucial for low‐power logical and integrated circuit applications.

A shock-stable rotated-hybrid Riemann solver on rectangular and triangular grids

The rotated Riemann solver is robust against the carbuncle phenomenon, especially for multidimensional computation. Moreover, hybrid techniques are usually used to enhance the stability of an accurate scheme by combining an accurate scheme with a diffusive scheme. This paper proposes a rotated-hybrid Riemann solver named the rotated-HLLC+ scheme. The scheme is developed by hybridizing the Harten–Lax–van Leer contact (HLLC) scheme with the advection upstream splitting method based on a flux vector splitting (AUSMV+) scheme by following the rotated Riemann solver approach. The unit vector n1 is calculated from the velocity-difference vector, and the unit vector n2 is the orthogonal vector. The linearized analysis suggests that the HLLC scheme should be used in the direction of n1 and the AUSMV+ scheme in the direction n2. In this way, the hybrid scheme becomes shock-stable with less numerical dissipation. Moreover, the pressure-based method is used to detect the shock wave. Several numerical experiments suggest that the pressure cutoff parameter εp=0.01 may be generally suitable and provide a stable solution with little additional numerical dissipation. The last two numerical examples show that the computational performance of the rotated-HLLC+ scheme is comparable to the HLLC scheme for the weak shock reflection over convex double wedges. However, the scheme is approximately 9% faster than the HLLC scheme for the double Mach reflection of a strong shock wave. The proposed scheme gives fast, stable, and accurate solutions on rectangular and triangular grids.

Passivating Contacts for Crystalline Silicon Solar Cells: An Overview of the Current Advances and Future Perspectives

AbstractSolar photovoltaics (PV) are poised to be crucial in limiting global warming by replacing traditional fossil fuel generation. Within the PV community, crystalline silicon (c‐Si) solar cells currently dominate, having made significant efficiency breakthroughs in recent years. These advancements are primarily due to innovations in solar cell technology, particularly in developing passivating contact schemes. As such, this review article comprehensively examines the evolution of high‐efficiency c‐Si solar cells, adopting a historical perspective to investigate the advancements in passivation contact techniques and materials to state‐of‐the‐art cell designs. Additionally, this work deeply studies the recent advances and critical design principles underlying each developed passivation scheme. Eventually, this work identifies existing challenges and proposes insights into future directions for c‐Si solar cells through diverse passivating contact strategies.

Low-resistivity Ohmic contacts of Ti/Al on few-layered 1T'-MoTe2/2H-MoTe2 heterojunctions grown by chemical vapor deposition.

This study explores the phase-controlled growth of few-layered 2H-MoTe2, 1T'-MoTe2, and 2H-/1T'-MoTe2 heterostructures and their impacts on metal contact properties. Cold-wall chemical vapor deposition (CW-CVD) with varying growth rates of MoOx and reaction temperatures with Te vapors enabled the growth of continuous thin films of either 1T'-MoTe2 or 2H-MoTe2 phases on two-inch sapphire substrates. This methodology facilitates the meticulous optimization of chemical vapor deposition (CVD) parameters, enabling the realization of phase-controlled growth of few-layered MoTe2 thin films and their subsequent heterostructures. The study further investigates the influence of a 1T'-MoTe2 intermediate layer on the electrical properties of metal contacts on few-layered 2H-MoTe2. Bi-layer Ti/Al contacts directly deposited on 2H-MoTe2 exhibited Schottky behavior, indicating inefficient carrier transport. However, introducing a few-layered 1T'-MoTe2 intermediate layer between the metal and 2H-MoTe2 layers improved the contact characteristics significantly. The resulting Al/Ti/1T'-MoTe2/2H-MoTe2 contact scheme demonstrates Ohmic behavior with a specific contact resistance of around 1.7 × 10-4 Ω cm2. This substantial improvement is attributed to the high carrier concentration of the 1T'-MoTe2 intermediate layer which could be attributed tentatively to the increased tunneling events across the van der Waals gap and enhancing carrier transport between the metal and 2H-MoTe2.

An explicit pseudo‐energy conservative scheme for contact between deformable solids

AbstractWe extend the work of Marazzato et al. [Int. J. Numer. Methods Eng, 121:5295‐5319] on elastodynamics to the treatment of contact. To that end, we propose adequate handling of boundary conditions, either through the resolution of local problems on each of the face displacement unknowns or through interpolation from nearest neighbours. Adapting the time‐integration strategy adopted in Marazzato et al. [Comput Methods Appl Mech Eng, 347:906‐927], it is possible to conserve both momentum and a pseudo‐energy exactly. Numerical results are presented to illustrate the accuracy of contact treatment and the energy conservation of the system.

When, how and why should we involve trusted contacts when serious concerns are raised about a student's well-being?

PurposeThis study investigates the relationship between mental well-being (MWB) and social support (SS) whilst addressing the paucity of research on students' support for emergency contact schemes (ECSs) and their views on how and when such schemes should be implemented.Design/methodology/approachIn total, 113 students recruited via opportunistic sampling completed an online survey including the Interpersonal Support Evaluation List - shortened version (Cohen et al. 1985), Warwick–Edinburgh Mental Wellbeing Scale (Tennant et al. 2007) and questions about ECS. A correlational design used the Pearson product-moment correlation to explore the relationship between MWB and SS. A between-subjects design using independent measures t-test investigated differences in SS and MWB between those with and without a “trusted person” (TP).FindingsThe preferred name was “Named Trusted Person Scheme” (NTPS), the preferred TP was parent/guardian or partner, and the preferred means of contact was Personal Tutor to mobile phone. Most students (96%) supported the use of an NTPS when serious concerns were raised about mental or physical health, personal safety or student engagement. Those opposed were concerned about a loss of agency, identifying a TP or the TP worsening the situation. MWB was positively correlated with SS, and those with a TP had higher levels of MWB and SS than those without.Originality/valueThis study addresses the under-explored area of students' support for ECS, whilst enhancing our understanding of the relationship between MWB and SS especially amongst those without a person they can trust. This research provides valuable insights for universities looking to implement or refine such schemes, with the potential to improve students' MWB, academic achievement and retention by enhancing support.

Recent Progress in Source/Drain Ohmic Contact with β-Ga2O3

β-Ga2O3, with excellent bandgap, breakdown field, and thermal stability properties, is considered to be one of the most promising candidates for power devices including field-effect transistors (FETs) and for other applications such as Schottky barrier diodes (SBDs) and solar-blind ultraviolet photodetectors. Ohmic contact is one of the key steps in the β-Ga2O3 device fabrication process for power applications. Ohmic contact techniques have been developed in recent years, and they are summarized in this review. First, the basic theory of metal–semiconductor contact is introduced. After that, the representative literature related to Ohmic contact with β-Ga2O3 is summarized and analyzed, including the electrical properties, interface microstructure, Ohmic contact formation mechanism, and contact reliability. In addition, the promising alternative schemes, including novel annealing techniques and Au-free contact materials, which are compatible with the CMOS process, are discussed. This review will help our theoretical understanding of Ohmic contact in β-Ga2O3 devices as well as the development trends of Ohmic contact schemes.

Minimisation of Parasitic Capacitance in Lumped-Element Electro-Absorption Modulators for High-Speed Optical Components

This paper presents an investigation into the parasitic capacitance of an RF contact scheme for lumped-element EAMs. Test structures are fabricated to analyse this parasitic capacitance via S11 characterisation using a vector network analyser (VNA). Optimisations of the contact scheme lead to the parasitic capacitance being reduced to <10 fF. EAMs using this contact scheme are fabricated and characterised using S11 measurements. These S11 measurements are used to simulate S21 measurements, which predict a f3dB bandwidth of near 80 GHz using an equivalent circuit model.

Low temperature electrical transport in thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition

In this paper electrical transport studies are performed on thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition (PLD) applying laser ablation of micro-crystalline graphite target. Experiments were carried out on 320 - 420 nm thick SiO2 on Si substrates as well as on hydrogenated diamond-like carbon (DLC) films deposited on SiO2/Si. Structural studies by means of XPS, SEM and Raman spectroscopy revealed that the films can be characterized as nano-sized carbon phases possessing different phase composition (i.e. the ratio sp3/sp2 hybridized carbon, etc.). The electrical conductivity/resistivity of the films was measured in the temperature range 10 K < T < 300 K. Four-contact Van der Pauw method as well as two contact schemes have been applied. Some films have low room temperature resistivity in the range ρ = (0.1–1.5)×10-3 Ω.·m and consist predominantly of sp2 hybridized carbon with Raman spectra, which resemble that of nano-sized graphene depending on the deposition conditions and substrates used. The thinnest only 0.5 nm layer deposited directly on SiO2 exhibits relatively low specific resistance (~10-3 Ω. m), which can be taken as an indication of good deposition conditions of graphene-like layers. The current flow mechanism was explored at temperatures from 300 K down to 10K. The temperature dependence reveals non-metallic behavior - the conductivity decreases at decreasing temperature as opposed to typical metal behaviour. A model of variable range hopping (VRH) mechanism is applied to explain the low temperature conductivity drawn from transport in nanocrystalline disordered systems.

Ag nanodot/Mg/Al reflective Ohmic contacts simultaneously suitable for n-type and p-type GaN

This work reports on high-reflectivity Ag nanodot (AgND)/Mg/Al Ohmic contacts suitable for both p-GaN and n-GaN. The lowest specific contact resistances are found to be 2.25 × 10−2 Ω·cm2 on p-GaN and 2.56 × 10−5 Ω·cm2 on n-GaN. Ag was deposited and converted into AgNDs by annealing, and Mg/Al was then deposited. A second annealing process at different temperatures was performed to check the thermal stability of the contacts. Both the p-GaN and n-GaN contacts were Ohmic after annealing at 300 °C or below. The AgND/Mg/Al contacts annealed at 250 °C or less showed a reflectivity of over 91% for wavelengths from 400 to 550 nm. X-ray photoelectron spectroscopy and x-ray diffraction measurements were performed to investigate the contact mechanisms. We propose that in AgND/Mg/Al on p-GaN, the effective barrier is lowered due to the presence of an Ag2O intermedia layer and the tunneling effect enables Ohmic contact. When the annealing temperature is 350 °C or higher, the Ag2O changes to β-AgGaO2 or is decomposed and the height and width of the barrier for holes increase, which causes the Ohmic contact to deteriorate. The Ohmic behavior of AgND/Mg/Al contacts on n-GaN is assumed to be mainly due to the high direct coverage ratio of Mg and the good Ohmic contact behavior of Mg/n-GaN. These results show that AgND/Mg/Al Ohmic contacts can be fabricated simultaneously on both p-GaN and n-GaN, which is a possible solution for improving the density of both GaN-based ICs and micro-light emitting diodes (LEDs). This contact scheme can also improve the light output efficiency of GaN-based LEDs.

DRL-assisted delay optimized task offloading in automotive-industry 5.0 based VECNs

The rapid growth of Automotive-Industry 5.0 and its emergence with beyond fifth-generation (B5G) communications, is making vehicular edge computing networks (VECNs) increasingly complex. The latency constraints of modern automotive applications make it difficult to run complex applications on vehicle on-board units (OBUs). While multi-access edge computing (MEC) can facilitate task offloading to execute these applications, it is still a challenge to access them promptly and optimally. Traditional algorithms struggle to guarantee accuracy in such dynamic environment, but deep reinforcement learning (DRL) methods offer improved accuracy, robustness, and real-time decision-making capabilities. In this paper, we propose a DRL-based mobility, contact, and load aware cooperative task offloading (DCTO) scheme. DCTO is designed for both cellular and mmWave radio access technologies (RATs), and both binary and partial offloading mechanisms. DCTO targets delay minimization by opportunistically switching RATs and offloading mechanisms. We consider relative efficacy and neutrality factors as key performance indicators and use them to derive the DRL agent’s reward function. Extensive evaluations demonstrate that the DCTO scheme exhibits a substantial enhancement in task success rate, with an increase from 2.61% to 21.34%. It also improves the efficacy factor from 1.38 to 3.52 and reduces the neutrality factor from 4.99 to 0.76. Furthermore, the average task processing time is reduced by a range of 3.77% to 24.15%. Additionally, the DCTO scheme outperforms the other evaluated schemes in terms of reward and TFPS ratio.

Intraoperative Local Field Potential Beta Power and Three-Dimensional Neuroimaging Mapping Predict Long-Term Clinical Response to Deep Brain Stimulation in Parkinson Disease: A Retrospective Study

BackgroundDirectional deep brain stimulation (DBS) leads allow a fine-tuning control of the stimulation field, however, this new technology could increase the DBS programming time because of the higher number of the possible combinations used in directional DBS than in standard nondirectional electrodes. Neuroimaging leads localization techniques and local field potentials (LFPs) recorded from DBS electrodes implanted in basal ganglia are among the most studied biomarkers for DBS programing. ObjectiveThis study aimed to evaluate whether intraoperative LFPs beta power and neuroimaging reconstructions correlate with contact selection in clinical programming of DBS in patients with Parkinson disease (PD). Materials and MethodsIn this retrospective study, routine intraoperative LFPs recorded from all contacts in the subthalamic nucleus (STN) of 14 patients with PD were analyzed to calculate the beta band power for each contact. Neuroimaging reconstruction obtained through Brainlab Elements Planning software detected contacts localized within the STN. Clinical DBS programming contact scheme data were collected after one year from the implant. Statistical analysis evaluated the diagnostic performance of LFPs beta band power and neuroimaging data for identification of the contacts selected with clinical programming. We evaluated whether the most effective contacts identified based on the clinical response after one year from implant were also those with the highest level of beta activity and localized within the STN in neuroimaging reconstruction. ResultsLFPs beta power showed a sensitivity of 67%, a negative predictive value (NPV) of 84%, a diagnostic odds ratio (DOR) of 2.7 in predicting the most effective contacts as evaluated through the clinical response. Neuroimaging reconstructions showed a sensitivity of 62%, a NPV of 77%, a DOR of 1.20 for contact effectivity prediction. The combined use of the two methods showed a sensitivity of 87%, a NPV of 87%, a DOR of 2.7 for predicting the clinically more effective contacts. ConclusionsThe combined use of LFPs beta power and neuroimaging localization and segmentations predict which are the most effective contacts as selected on the basis of clinical programming after one year from implant of DBS. The use of predictors in contact selection could guide clinical programming and reduce time needed for it.